1. Field of the Invention
The present invention relates to an evaporator assembly apparatus, and in particular, although not exclusively, to an evaporator assembly for incorporation into an air conditioning apparatus for use in automobiles.
2. Discussion of the Prior Art
In automobiles, air conditioning systems are utilised to provide space cooling within a passenger compartment, by introduction of cooled air. The introduced air may be either fresh air from outside the vehicle, or air from within the passenger compartment which has been withdrawn therefrom and cooled by the air conditioning apparatus, or a mixture thereof. A conventional air conditioning apparatus employs an evaporator assembly comprising evaporative heat exchanger consisting of a plurality of tubes through which coolant is passed, mounted in an air duct, and a fan to provide forced passage of air through the duct, which air is cooled on contact with the tubes of the heat exchanger. An example of an air conditioning apparatus which is for use in motor trucks is disclosed in European Patent Application Published No 043668.
Although such a system can operate effectively under conditions of high load such as will exist on initial cooling, the effectiveness of the cooling operation decreases rapidly as the temperatures of the heat exchanger and the inlet air converge. This decline of cooling is particularly dramatic when the inlet air is drawn from the space to be conditioned. This manifests itself as a rapid decline in the refrigerant flow rate after initial switching on of the refrigerating circuit during a peak demand condition. Typically, for a conventional evaporator in an automobile, the flow rate decline may be of the order of 28% after about two and a half minutes, and a further 18% after a further fifteen minutes. Whilst the condensing and pumping components of the heat exchanger circuit can maintain the throughput of refrigerant, the flow rate is limited by the rate of heat transfer of the heat exchanger. There is therefore a need to increase the efficiency of the heat exchanger. Whilst a heat exchanger which is deeper in the direction of air flow will allow a greater rate of heat transfer, the increased dimensions are undesirable; compactness of the heat exchanger, weight and cost thereof are of great importance, particularly for use in automobiles.
Moreover, it can be shown that the quantity of refrigerant charge required in the heat exchanger circuit is that which will satisfy the evaporative heat exchanger under all encountered load and operating conditions, plus an equal volume in the remainder of the circuit, plus a small amount which is required to counteract anticipated leakage from the system. Therefore, if the volume of the evaporator heat exchanger can be reduced, the total quantity of refrigerant required for the system can be reduced by about twice the evaporator heat exchanger volume reduction, further reducing the cost.
It is an object of the invention to provide an air conditioning apparatus which overcomes the problems referred to above, and which is of particularly overall compact design.